Herbicidal amide compositions

ABSTRACT

A composition comprising compounds of the formula ##EQU1## wherein R 1  and R 2  each is alkyl; R 3  is substituted carbamoyl or thiocarbamoyl; and R 4  is optionally substituted phenyl, are useful as herbicides.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Ser. No. 482,936, filed June 25, 1974, now U.S. Pat. No. 3,891,675, issued June 24, 1975.

DESCRIPTION OF THE INVENTION

This invention relates to amide derivatives which are of interest as herbicides.

Accordingly the present invention provides amide derivatives of general formula: ##STR1## wherein R₁ and R₂ each represents an alkyl group; R₃ represents a carbamoyl or thiocarbamoyl group N-substituted by alkyl, haloalkyl, cycloalkyl, phenyl, alkylphenyl, halophenyl, nitrophenyl, alkoxyphenyl or by alkenyl of 2 to 6 carbon atoms, and R₄ represents a phenyl group optionally substituted by halogen or by alkyl.

More particularly, the invention is directed to amide derivatives of general formula I wherein R₁ and R₂ each represents an alkyl group of 1-6 carbon atoms; R₃ represents a carbamoyl or thiocarbamoyl group N-substituted by alkyl, haloalkyl or cycloalkyl of up to 6 carbon atoms, by phenyl, alkylphenyl, nitrophenyl, alkoxyphenyl or fluoro- or chlorophenyl of up to 8 carbon atoms, and R₄ represents a phenyl group optionally substituted by fluorine or chlorine or by an alkyl group of 1-6 carbon atoms.

Examples of such compounds include those species described in Examples 1-20 hereinafter; also, the following species are contemplated, as well:

N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-(2-nitrophenyl)urea

N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-(3-methoxyphenyl)urea

N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-chloromethylurea

N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-methylthiourea

N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-phenylthiourea

Because of their properties, preferred amide derivatives are those of formula I wherein R₁ and R₂ each represents an alkyl group of 1-6 carbon atoms, for example methyl, ethyl, or propyl; R₃ represents a carbamoyl group N-substituted by alkyl or cycloalkyl of up to 6 carbon atoms, for example by methyl or by cyclohexyl, or by phenyl, tolyl or dichlorophenyl; and R₄ represents a phenyl group optionally substituted by one or two chlorine atoms or by an alkyl group of 1-6 carbon atoms, for example by methyl.

Especially active, and therefore especially effective amide derivatives appear to be those of formula I wherein R₁ represents metyl, ethyl or propyl; R₂ represents methyl; R₃ represents a carbamoyl group N-substituted by methyl, ethyl, propyl or butyl; and R₄ represents phenyl optionally substituted by one or two chlorine.

Preferred species of this subclass include:

N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'methylurea

N-((4-benzyloxymethyl-2-methyl-4-n-propyl-1,3-dioxolan-2-yl)carbonyl)-N'methylurea

N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxolan-2-yl)carbonyl)-N'butylurea

It has also been found that compounds of formula I wherein R₃ is N-substituted carbamoyl and the R₄ phenyl group is substituted at the 2-position (ortho position) by fluorine have highly useful herbicidal activity. Examples of such useful compounds are:

N-(4-(2-fluorobenzyloxymethyl 2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N-phenylurea

N-(2-fluorobenzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N.sup.1 -butylurea

The compounds of formula I may be prepared by a process which comprises reacting a compound of formula I wherein R₃ represents a hydrogen atom with an isocyanate of the formula R₆ NCO or an isothiocyanate of formula R₆ NCS wherein R₆ represents an alkyl, haloalkyl, cycloalkyl, phenyl, alkylphenyl, halophenyl, nitrophenyl, alkoxyphenyl or alkenyl group. The cmpounds of formula I wherein R₃ is hydrogen are known compounds, disclosed in Netherlands Pat. No. 72,07026.

As mentioned above the amide derivatives of the invention are of interest as herbicides, and the invention includes, therefore, herbicidal compositions comprising a carrier and/or a surface active agent, together with, as active ingredient, an amide derivative of the invention. Likewise the invention also includes a method of combating weeds at a locus which comprises applying to the locus an amide derivative or composition of the invention.

The term "carrier" as used herein means a solid or fluid material, which may be inorganic or organic and of synthetic or natural origin, with which the active compound is mixed or formulated to facilitate its application to the plant, seed, soil or other object to be treated, or its storage, transport or handling.

The surface-active agent may be an emulsifying agent or a dispersing agent or a wetting agent; it may be non-ionic or ionic.

Any of the carrier materials or surface-active agents usually applied in formulating pesticides may be used in the compositions of the invention, and suitable examples of these are to be found, for example, in UK patent specification No. 1,232,930.

The compositions of the invention may be formulated as wettable powders, dusts, granules, solutions, emulsifiable concentrates, emulsions, suspension concentrates or aerosols. Wettable powders are usually compounded to contain 25, 50 or 75% w of toxicant and usually contain, in addition to solid carrier, 3-10% w of a dispersing agent and, where necessary, 0-10% w of stabiliser(s) and/or other additives such as penetrants or stickers. Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant, and are diluted in the field with further solid carrier to give a composition usually containing 178 -10% w of toxicant. Granules are usually prepared to have a size between 10 and 100 BS mesh (1.676-0.152 mm), and may be manufactured by agglomeration or impregnation techniques. Generally, granules will contain 1/2-25% w active ingredient and 0-10% w of additives such as stabilisers, slow release modifiers and binding agents. Emulsifiable concentrates usually contain, in addition to the solvent and, when necessary, co-solvent, 10-50% w/v active ingredient, 2-20% w/v emulsifiers and 0-20% w/v of appropriate additives such as stabilisers, penetrants and corrosion inhibitors. Suspension concentrates are compounded so as to obtain a stable, non-sedimenting, flowable product and usually contain 10-75% w active ingredient, 0.5-15% w of dispersing agents, 0.1-10% w of suspending agents such as protective colloids and thixotropic agents, 0-10% w of appropriate additives such as defoamers, corrosion inhibitors, stabilisers, penetrants and stickers, and as carrier, water or an organic liquid in which the active ingredient is substantially insoluble; certain organic solids or inorganic salts may be dissolved in the carrier to assist in preventing sedimentation or as antifreeze agents for water.

Aqueous dispersions and emulsions, for example, compositions obtained by diluting a wettable powder or a concentrate according to the invention with water, also lie within the scope of the present invention. The said emulsions may be of the water-in-oil or of the oil-in-water type, and may have a thick "mayonnaise"-like consistency.

The compositions of the invention may also contain other ingredients, for example, other compounds possessing pesticidal, especially insecticidal, acaricidal, herbicidal or fungicidal properties.

The invention is further illustrated by the following examples. It should be understood, however, that the examples are for the purpose of illustration only and should not be regarded as limiting the invention in any way. In the examples the structure of the compounds was confirmed by elemental analysis and NMR spectral analysis.

EXAMPLE 1 N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxolane-2-yl)carbonyl)-N-phenylurea

4-Benzyloxymethyl-2,4-dimethyl-1,3-dioxane-2-carboxamide (4.5g) and phenyl isocyanate (2.0g) in toluene (50 ml) were heated together under reflux for 20 hours. The toluene was then removed from the mixture under reduced pressure. The residue was triturated with petroleum ether (b.p. 40°-60° C) and recrystallized from ethanol to give the required product m.p. 91°-94° C.

EXAMPLES 2-25

Following procedures similar to those given in the previous Example further compounds were prepared, for which physical characteristics are given in Table 1.

                                      TABLE 1                                      __________________________________________________________________________                                   m.p.° C                                                                 or                                               Example                                                                               Compound               refractive index                                 __________________________________________________________________________      2   N-((4-benzyloxymethyl-4-ethyl-2-methyl-1,3-                                                             m.p.                                                  dioxolan-2-yl)carbonyl)-N'-phenylurea                                                                   100-102                                           3   N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxo-                                                           m.p.                                                  lan-2-yl)carbonyl)-N'-(3,4-dichlorophenyl)urea                                                          129-134                                           4   N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxo-                                                           m.p.                                                  lan-2-yl)carbonyl)-N'-(m-tolyl)urea                                                                     107-110                                               isomer A                                                                   5   N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxo-                                                           n.sub.D.sup.24 1.5237                                 lan-2-yl)carbonyl)-N'(m-tolyl)urea                                             isomer B                                                                   6   N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxo-                                                           m.p.                                                  lan-2-yl)carbonyl)-N'-cyclohexylurea                                                                    120-122                                           7   N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxo-                                                           m.p.                                                  lan-2-yl)carbonyl)-N'-methylurea                                                                        113-116                                           8   N-((4-benzyloxymethyl-4-ethyl-2-methyl-1,3-                                                             m.p.                                                  dioxolan-2-yl)carbonyl)-N'-methylurea                                                                   124-126                                           9   N-((4-benzyloxymethyl-2-methyl-4-propyl-1,3-                                                            m.p.                                                  dioxolan-2-yl)carbonyl)-N'-methylurea                                                                   110-112                                          10   N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxo-                                                           m.p.                                                  lan-2-yl)carbonyl)-N'-butylurea                                                                         76-78                                            11   N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxo-                                                           m.p.                                                  lan-2-yl)carbonyl)-N-ethylurea                                                                          85-91                                            12   N-(4-(2,6-dichlorobenzyloxymethyl)-4-ethyl-2-                                                           m.p.                                                  methyl-1,3-dioxolan-2-yl)carbonyl)-N'-                                                                  109-121                                               methylurea                                                                13   N-((4-benzyloxymethyl)-4-ethyl-2-methyl-1,3-                                                            m.p.                                                  dioxolan-2-ylcarbonyl)-N'-ethylurea                                                                     111-114                                          14   N-(4-benzyloxymethyl-4-ethyl-2-methyl-1,3-                                                              m.p.                                                  dioxolan-2-ylcarbonyl)-N'-butenylurea                                                                   96-100                                           15   N-(4-benzyloxymethyl-2-methyl-4-n-propyl-                                                               m.p.                                                  1,3-dioxolan-2-ylcarbonyl)-N'-phenylurea                                                                91-93                                            16   N-(4-(4-fluorobenzyloxymethyl)-4-ethyl-2-                                                               m.p.                                                  methyl-1,3-dioxolan-2-ylcarbonyl)                                                                       90-93                                                 phenylurea                                                                     isomer mixture                                                            17   N-(4-(4-fluorobenzyloxymethyl)-4-ethyl-2-                                                               m.p.                                                  methyl-1,3-dioxolan-2-ylcarbonyl)-N'  -                                                                 110-112                                               phenylurea                                                                     isomer B                                                                  18   N-(4-(4-fluorobenzyloxymethyl)-4-ethyl-2-                                                               m.p.                                                  methyl-1,3-dioxolan-2-ylcarbonyl)-N'-                                                                   84-86                                                 butylurea                                                                      isomer B                                                                  19   N-(4-fluorobenzyloxymethyl-4-ethyl-2-methyl-                                                            m.p.                                                  1,3-dioxolan-2-ylcarbonyl)-N'-(3,4-dichloro-                                                            118-120                                               phenyl)urea                                                                    isomer B                                                                  20   N-(4-fluorobenzyloxymethyl-4-ethyl-2-methyl-                                                            m.p.                                                  1,3-dioxolan-2-ylcarbonyl)-N'-(3,4-dichloro-                                                            97-107                                                phenyl)urea                                                                    isomer mixture                                                            21   N-(4-(2-fluorobenzyloxymethyl-2-methyl-                                                                 m.p.                                                  4-ethyl-1,3-dioxolan-2-yl)carbonyl)-                                                                    80-85                                                 N.sup.1 -phenylurea                                                            isomer mixture                                                            22   N-(4-(2-fluorobenzyloxymethyl)-2-methyl-4-                                                              m.p.                                                  ethyl-1,3-dioxolan-2-ylcarbonyl)-N.sup.1 -                                                              86-88                                                 butylurea                                                                      isomer 1                                                                  23   N-(4-(2-fluorobenzyloxymethyl)-2-methyl-4-                                                              m.p.                                                  ethyl-1,3-dioxolan-2-ylcarbonyl)-N.sup.1 -                                                              108-112                                               (3,4-dichlorophenyl)urea                                                       isomer 2                                                                  24   N-(4-(2-fluorobenzyloxymethyl)-2-methyl-                                                                m.p.                                                  4-ethyl-1,3-dioxolan-2-ylcarbonyl)-N.sup.1 -                                                            --                                                    (3-methylphenyl)urea                                                           isomer 1                                                                  25   N-(4-(2-fluorobenzyloxymethyl)-2-methyl-                                                                m.p.                                                  4-ethyl-1,3-dioxolan-2-ylcarbonyl)-N.sup.1 -                                                            --                                                    (3-methylphenyl)urea                                                           isomer 2                                                                  __________________________________________________________________________

EXAMPLE 26 Herbicidal Activity

To evaluate their herbicidal activity, compounds of the invention were tested using as a representative range of plants:- maize, Zea mays (MZ); rice, oryza sativa (R); barnyard grass, Echinchloa crusgalli (BG); pea, Pisum sativum (P); linseed, Linum usitatissium (L); mustard, Sinapis alba (M); and sugar beet, Beta vulgaris (SB).

The tests fall into two categories, pre-emergence and post-emergence. The pre-emergence tests involved spraying a liquid formulation of the compound onto the soil in which the seeds of the plant species mentioned above had recently been sown. The post-emergence tests involved two types of test, viz. soil drench and foliar spray tests. In the soil drench tests the soil in which seedling plants of the above species were growing, was drenched with a liquid formulation containing a compound of the invention, and in the foliar spray tests the seedling plants were sprayed with such a formulation.

The soil used in the tests was a steam-sterilized, modified John Innes Compost mixture in which half the peat, by loose bulk, had been replaced by vermiculite.

The formulations used in the tests were prepared by diluting with water solutions of the compounds in acetone containing 0.4% by weight of an alkylphenol/ethylene oxide condensate available under the trade name Triton X-155. In the soil spray and foliar spray tests the acetone solutions were diluted with an equal volume of water and the resulting formulations applied at two dosage levels corresponding to 10 and 1 kilograms of active material per hectare respectively in a volume equivalent to 400 liters per hectare or in some cases at two dosage levels corresponding to 5 and 1 kilogram of active material per hectare, respectively, as indicated. In the soil drench tests one volume of the acetone solution was diluted to 155 volumes with water and the resulting formulation applied at one dosage level equivalent to 10 kilograms of active material per hectare in a volume equivalent to approximately 3,000 liters per hectare.

The herbicidal effects of the compounds were assessed visually seven days after spraying the foliage and drenching the soil and eleven days after spraying the soil, and were recorded on a 0-9 scale. A rating 0 indicates no effect on the treated plants, a rating 2 indicates a reduction in fresh weight of stem and leaf of the plants of approximately 25%, a rating 5 indicates a reduction of approximately 55%, a rating 9 indicates a reduction of 95% etc.

The results of the tests are set out in Table 2 and 3.

                                      TABLE 2                                      __________________________________________________________________________              Post-emergence                Pre-emergence                           Dosage   Soil Drench    Foliar Spray   Soil Spray                              Example                                                                             kg/ha                                                                              Mz                                                                               R BG P L M SB                                                                               Mz                                                                               R BG P L M SB                                                                               Mz                                                                               R BG P L M SB                         __________________________________________________________________________     1    10  5 5 7  2 6 3 4 3 2 7  3 6 4 2 8 9 9  9 7 5 2                               1                  3 0 7  3 6 4 0 6 9 9        7                                                                              7                                                                              3                                                                              1                          2    10  7 5 8  1 7 3 2 4 3 7  3 7 3 2 7 8 9        9                                                                              8                                                                              4                                                                              4                               1                  0 0 6  3 7 3 0 4 7 9        9                                                                              7                                                                              3                                                                              3                          3    10  0 2 8  0 5 0 0 0 0 7  2 6 3 0 3 7 9        8                                                                              7                                                                              6                                                                              5                               1                  0 0 6  2 6 3 0 1 5 9        8                                                                              7                                                                              5                                                                              3                          4    10  0 0 7  0 0 0 0 1 0 2  3 6 3 1 2 3 8        0                                                                              7                                                                              2                                                                              0                               1                  0 0 0  2 6 3 0 0 0 7        0                                                                              2                                                                              0                                                                              0                          5    10  7 6 8  1 7 4 0 5 1 7  3 7 5 4 8 9 9        9                                                                              8                                                                              8                                                                              0                               1                  2 0 5  2 7 5 3 6 8 9        5                                                                              8                                                                              2                                                                              0                          6    10  7 6 8  2 7 2 0 6 2 7  2 7 4 0 8 9 9        9                                                                              8                                                                              6                                                                              0                               1                  3 0 5  1 7 2 0 8 9 9        8                                                                              8                                                                              5                                                                              0                          7    10  7 7 8  4 7 3 3 6 6 7  3 8 4 2 9 9 9        9                                                                              8                                                                              8                                                                              8                               1                  5 4 6  2 6 1 0 9 9 9        9                                                                              8                                                                              8                                                                              8                          8    10  8 9 8  4 9 6 4 7 8 8  5 8 5 5 9 9 9        9                                                                              9                                                                              8                                                                              7                               1                  5 6 6  3 7 3 3 9 9 9        8                                                                              8                                                                              8                                                                              4                          9    10  8 9 8  4 8 4 4 8 7 8  4 8 5 6 9 9 9        8                                                                              8                                                                              9                                                                              7                               1                  5 5 6  3 4 3 4 9 9 9        8                                                                              7                                                                              6                                                                              0                          10   10  9 7 9  9 8 6 8 7 6 9  9 7 5 4 9 9 9        7                                                                              8                                                                              8                                                                              4                               1                  6 5 8  0 6 5 4 8 7 9        5                                                                              7                                                                              8                                                                              7                          11   10  9 8 9  9 9 6 3 6 5 8  4 7 4 4 9 9 9        9                                                                              8                                                                              8                                                                              5                               1                  6 5 8  4 6 4 4 9 8 9        8                                                                              8                                                                              8                                                                              4                          12   10  6 6 7  2 3 5 4 6 2 8  4 7 5 6 8 8 9        7                                                                              7                                                                              5                                                                              1                               1                  6 0 5  4 4 2 2 6 6 9        6                                                                              5                                                                              5                                                                              0                          13   10  7 6 7  7 6 6 4 7 6 8  4 6 4 6 9 9 9        8                                                                              7                                                                              8                                                                              5                               1                  6 5 8  2 5 3 3 7 9 9        8                                                                              7                                                                              7                                                                              2                          14   10  7 6 8  3 6 3 2 6 4 8  2 4 4 0 8 9 9        7                                                                              7                                                                              7                                                                              2                               1                  4 1 7  1 4 3 0 7 8 9        3                                                                              7                                                                              6                                                                              1                          __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________              Post-Emergence                    Pre-Emergence                       Example                                                                             Dosage                                                                             Soil Drench    Dosage                                                                             Folair Spray   Soil Spray                          No.  kg/ha                                                                              Mz                                                                               R BG P L M SB                                                                               kg/ha                                                                              Mz                                                                               R BG P L M SB                                                                               Mz                                                                               R BG P L M SB                     __________________________________________________________________________     21   10  6 4 7  3 3 5 4 5   4 0 7  7 7 5 2 2 4 9  8 7 6 3                            1                 1   1 0 7  7 7 2 0 2 4        9                                                                              7                                                                              7                                                                              6 3                      22   10  7 5 7  6 5 5 2 5   6 4 7  7 7 5 2 7 9        9                                                                              9                                                                              7                                                                              6 3                            1                 1   4 1 7  7 7 4 0 6 8        9                                                                              8                                                                              7                                                                              6 3                      23   10  1 0 7  2 0 0 0 5   2 0 6  6 7 5 6 0 2        9                                                                              1                                                                              2                                                                              5 9                            1                 1   0 0 3  3 6 4 4 0 0        8                                                                              0                                                                              2                                                                              4 0                      24   10  0 0 0  0 0 0 0 5   3 0 7  6 5 6 4 1 1        9                                                                              0                                                                              5                                                                              3 0                            1                 1   1 0 4  3 4 3 2 0 0        3                                                                              0                                                                              0                                                                              0 0                      25   10  7 2 8  2 0 0 1 5   5 1 8  7 7 6 6 7 6        9                                                                              8                                                                              8                                                                              6 3                            1                 1   2 0 8  7 7 5 5 6 4        9                                                                              7                                                                              8                                                                              6 3                      __________________________________________________________________________ 

We claim as our invention:
 1. A method of combating weeds at a locus which comprises applying to that locus a herbicidally effective amount of an amide derivative of formula I ##EQU2## wherein R₁ and R₂ each represents an alkyl group; R₃ represents a carbamoyl or thiocarbamoyl group N-substituted by alkyl, haloalkyl, cycloalkyl, phenyl, alkylphenyl, halophenyl, nitrophenyl, alkoxyphenyl or by alkenyl of 2 to 6 carbon atoms; and R₄ represents a phenyl group optionally substituted by halogen or by alkyl, or a composition thereof.
 2. A method according to claim 1 wherein R₁ and R₂ each represents an alkyl group of 1 to 6 carbon atoms; R₃ represents a carbamoyl or thiocarbamoyl group N-substituted by alkyl, haloalkyl or cycloalkyl of up to 6 carbon atoms, by phenyl, alkylphenyl, nitrophenyl, alkoxyphenyl, or fluoro -- or chlorophenyl of up to 8 carbon atoms, or by alkenyl of 2 to 6 carbon atoms, and R₄ represents a phenyl group optionally substituted by fluorine or chlorine or by an alkyl group of 1 to 6 carbon atoms.
 3. A method according to claim 2 wherein R₃ represents a carbamoyl group N-substituted by alkyl or cycloalkyl of up to 6 carbon atoms, or by phenyl, tolyl or dichlorophenyl; and R₄ represents a phenyl group optionally substituted by one or two chlorine atoms or by an alkyl group of 1 to 6 carbon atoms.
 4. A method according to claim 3 wherein R₁ represents methyl, ethyl or propyl; R₂ represents methyl; R₃ represents carbamoyl N-substituted by methyl, ethyl, propyl or butyl; and R₄ represents phenyl optionally substituted by one or two chlorine atoms.
 5. A method according to claim 2 in which the amide derivative is selected from N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-methylurea; N-((4-benzyloxymethyl-2-methyl-4-propyl-1,3-dioxolan-2-yl)carbonyl)-N'-methylurea; N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxolan-2-yl)carbonyl)-N'-butylurea; N-((4-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-ethylurea, N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxolan-2-yl)carbonyl)-N'-cyclohexylurea, N-((4-benzyloxymethyl-2,4-dimethyl-1,3-dioxolan-2-yl)carbonyl)-N'-ethylurea, N-((4-fluorobenzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-phenylurea or N-((4-(2,6-dichloro)benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-methylurea.
 6. A method according to claim 2 wherein the amide derivative is selected from N-((4-(2-fluoro)-benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-phenylurea or N-((4-(2-fluoro)benzyloxymethyl-2-methyl-4-ethyl-1,3-dioxolan-2-yl)carbonyl)-N'-butylurea.
 7. A method according to claim 1 wherein R₃ is an N-substituted carbamoyl group and R₄ is 2-fluorophenyl.
 8. A method according to claim 7 wherein R₁ and R₂ each represents an alkyl group of 1 to 6 carbon atoms and R₃ represents a carbamoyl group N-substituted by alkyl of up to 6 carbon atoms, or by phenyl, tolyl or dichlorophenyl.
 9. A method according to claim 8 wherein R₁ represents methyl, ethyl or propyl; R₂ represents methyl and R₃ represents carbamoyl N-substituted by butyl, phenyl, dichlorophenyl or tolyl.
 10. A herbicidal composition comprising a herbicidally effective amount of a compound of formula I as shown in claim 1 together with at least one carrier or surface active agent therefore. 